Geo: Add value transformation logic method

What does this MR do and why?

Simplify how gitlab's geo feature handles registry class name transformations, introduce a new method graphql_enum_key in the BaseRegistry class that encapsulates the value transformation logic.

This is a refactoring change and doesn't affect functionality.

Issue: #414370 (closed)

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ee/app/models/geo/base_registry.rb

@@ -91,7 +91,7 @@ def self.graphql_mutable?
     true
   end
 
-  # Method to generate a GraphQL enum key based on registery class.
+  # Method to generate a GraphQL enum key based on registry class.
   def self.graphql_enum_key
     self.to_s.gsub('Geo::', '').underscore
   end